digitoxin and bufalin

Sodium taurocholate cotransporting polypeptide (NTCP) has been reported as a functional receptor for hepatitis B virus (HBV) infection. However, HBV could not efficiently infect HepG2 cells expressing NTCP (NTCP-HepG2 cells) under adherent monolayer-cell conditions. In this study, NTCP was mainly detected in the basolateral membrane region, but not the apical site, of monolayer NTCP-HepG2 cells. We hypothesized that non-adherent cell conditions of infection would enhance HBV infectivity. Non-adherent NTCP-HepG2 cells were prepared by treatment with trypsin and EDTA, which did not degrade NTCP in the membrane fraction. HBV successfully infected NTCP-HepG2 cells at a viral dose 10 times lower in non-adherent phase than in adherent phase. Efficient infection of non-adherent NTCP-HepG2 cells with blood-borne or cell-culture-derived HBV was observed and was remarkably impaired in the presence of the myristoylated preS1 peptide. HBV could also efficiently infect HepaRG cells under non-adherent cell conditions. We screened several compounds using our culture system and identified proscillaridin A as a potent anti-HBV agent with an IC50 value of 7.2 nM. In conclusion, non-adherent host cell conditions of infection augmented HBV infectivity in an NTCP-dependent manner, thus providing a novel strategy to identify anti-HBV drugs and investigate the mechanism of HBV infection.

Topics: Antiviral Agents; Bufanolides; Cell Adhesion; Digitoxin; Digoxin; Gene Expression; Hep G2 Cells; Hepatitis B virus; High-Throughput Screening Assays; Humans; Organic Anion Transporters, Sodium-Dependent; Phthalazines; Proscillaridin; Receptors, Virus; Simvastatin; Strophanthins; Symporters; Transgenes; Viral Envelope Proteins; Virus Internalization

Intoxication caused by digitalis-like substances after ingestion of cooked toad soup has been reported. Bufalin, a cardioactive compound, is found in toad. Bufalin is also found in many Chinese medicines. Earlier reports demonstrated cross reactivity of bufalin with fluorescence polarization immunoassay for digoxin. In this report, the authors demonstrated a significantly higher cross reactivity of bufalin with the fluorescence polarization assay for digitoxin. They supplemented aliquots of normal plasma that had various concentrations of bufalin (1 to 50 micrograms/ml) from a local blood bank and measured apparent digitoxin concentrations using fluorescence polarization immunoassay and chemiluminescent assays (ACS digitoxin) for digitoxin. They measured apparent digoxin and digitoxin concentrations using fluorescence polarization, microparticle enzyme immunoassay, and chemiluminescent assays for digitoxin. They observed apparent digitoxin or digoxin concentrations in sera supplemented with bufalin only with the fluorescence polarization assays. For example, the apparent digitoxin concentration observed in a serum supplemented with 25 ng/ml of bufalin was 24.3 ng/ml of digitoxin equivalent. The apparent digoxin concentration observed in the same specimen was 1.33 ng/ml digoxin equivalent. Bufalin caused positive interference in serum digoxin or digitoxin measurements in specimens containing digoxin or digitoxin when concentrations were measured by fluorescence polarization assays. In contrast, bufalin lowered the measured digoxin concentrations in serum pools containing digoxin when digoxin concentrations were measured by the microparticle enzyme immunoassay. The authors conclude that bufalin toxicity can be rapidly detected by the fluorescence polarization assay for digitoxin.

Topics: Animals; Anura; Bufanolides; Cardiotonic Agents; Digitoxin; Digoxin; Drug Interactions; Fluorescence Polarization Immunoassay; Humans

The microparticle enzyme immunoassay (MEIA for digoxin (Abbott Laboratories, Abbott Park, Ill) requires no sample pretreatment and is widely used in clinical toxicology laboratories for monitoring serum digoxin concentrations. One advantage of the new MEIA is the lower cross-reactivities with such cross-reactants as digitoxin, oleandrin, and bufalin compared with the fluorescence polarization immunoassay (FPIA)for digoxin. Digitoxin, oleandrin, and bufalin showed positive cross-reactivity with MEIA and FPIAs for digoxin in the absence of the primary analyte, digoxin. A surprising finding was that digoxin concentrations were falsely decreased by these cross-reactants when serum pools containing digoxin were supplemented with various concentrations of these cross-reactants and when digoxin concentrations were measured by the MEIA. In contrast, digoxin concentrations were falsely elevated when measured by the FPIA. For example, when a serum pool containing 2.15 nmol/L of digoxin was supplemented with 129.5 nmol/L of bufalin, the apparent digoxin concentrations were 1.45 nmol/L with the MEIA and 3.00 nmol/L with the FPIA. Taking the advantage of only 25% protein binding of digoxin and more than 95% protein binding of digitoxin and bufalin, we demonstrated that monitoring free digoxin instead of total digoxin eliminated negative interference of digoxin by these cross-reactants in the MEIA and positive interference in the FPIA. Although oleandrin is also strongly bound to serum protein, high concentrations of oleandrin still modestly affect the free digoxin assay for both MEIA and FPIAs.

Topics: Bufanolides; Cardenolides; Cardiac Glycosides; Cardiotonic Agents; Cross Reactions; Digitoxin; Digoxin; False Positive Reactions; Fluorescence Polarization Immunoassay; Humans; Immunoenzyme Techniques; Microspheres

Oleandrin plant poisoning is common in children and the plant extract is used in Chinese medicines. The toxicity is due to oleandrin and the deglycosylated metabolite oleandrigenin. Bufalin and cinobufotalin (toad cardiac toxins) are also widely used in Chinese medicines like Chan SU, and Lu-Shen -WU. Severe toxicity from bufalin after consumption of toad soup has been reported. Taking advantage of structural similarities of these toxins with digitoxin, we demonstrated that these compounds can be rapidly detected in blood by the fluorescence polarization immunoassay for digitoxin. The cross reactivities of these compounds with digoxin assay were much lower. For example, when a drug free serum was supplemented with 10 microg/ml of oleandrin, we observed 127.7 ng/ml of digitoxin equivalent but only 2.4 ng/ml of digoxin equivalent concentration. Digibind neutralized all cardiac toxins studied as evidenced by significant fall of free concentrations. When aliquots of serum pool containing 50.0 microg/ml of oleandrin were supplemented with 0, 10.0, 25.0, 50.0, 100, and 200 microg/ml of digibind, the mean free concentrations were 30.6, 23.3, 16.0, 10.7, 7.8 and 5.5 microg/ml respectively. Similarly, with 50.0 microg/ml of oleandrigenin (total concentration: 36.2 ng/ml), the free concentration was 14.5 ng/ml digitoxin equivalent in the absence of digibind and 5.4 ng/ml in the presence of 200 microg/ml of digibind. In another specimen containing 500 ng/ml bufalin (total concentration: 156.9 ng/ml), the free concentration was 8.6 ng/ml in the absence of digibind and none detected in the presence of 100.0 microg/ml digibind. Because such neutralization may also occur in vivo, digibind may be useful in treating patients exposed to these toxins.

Topics: Bufanolides; Cardenolides; Cardiotonic Agents; Chromatography, High Pressure Liquid; Cross Reactions; Digitoxin; Digoxin; Humans; Immunoassay; Immunoglobulin Fab Fragments; Mass Spectrometry; Neutralization Tests

Efforts to study the endogenous sodium pump inhibitor (ESPI) have been complicated by the limited specificity of available assays. We recently developed an assay of [Na,K]ATPase inhibition more sensitive than conventional assays. This enhancement reflects a prereaction step that increases binding affinity of digitalislike molecules to the digitalis receptor. We tested the possibility that this enhanced inhibition is limited to inhibitors acting specifically through the digitalis-binding site. Using both the standard and sensitive [Na,K]ATPase methods, known specific inhibitors of the sodium pump (ouabain, digoxin, bufalin) showed significant increases in the inhibition in the sensitive as compared with the standard [Na,K]ATPase assay (ouabain 34.4 +/- 7.3 vs. 8.3 +/- 0.5%, digoxin 43.2 +/- 9.1 vs. 7.2 +/- 3.1%, bufalin 46.9 +/- 5.0 vs. 22.6 +/- 1.6%). Some proposed candidates for the ESPI, acknowledged to be nonspecific inhibitors, showed no enhancement (oleic acid 36.0 +/- 4.5 vs. 34.8 +/- 5.6%, lysophosphatidyl choline 10.8 +/- 3.5 vs. 12.8 +/- 5.2%, and vanadate 34.3 +/- 8.8 vs. 33.8 +/- 1.4%). Other candidates, whose inhibitory specificity is unknown, including an ESPI from the peritoneal dialysate of patients with renal failure were also studied. The ESPI showed enhanced inhibition (24.1 +/- 4.9 vs. 5.3 +/- 2.0%). These studies suggest that the sensitive assay in conjunction with a standard [Na,K]ATPase assay may allow the early determination of candidates interacting specifically with the digitalis receptor to inhibit the sodium pump.

Topics: Animals; Antineoplastic Agents; Binding, Competitive; Bufanolides; Cattle; Digitalis; Digoxin; Dose-Response Relationship, Drug; Enzyme Inhibitors; Kidney; Lysophosphatidylcholines; Oleic Acid; Oleic Acids; Ouabain; Plants, Medicinal; Plants, Toxic; Regression Analysis; Silver Nitrate; Sodium-Potassium-Exchanging ATPase; Steroids; Tamoxifen; Vanadates

Topics: Animals; Anura; Bufanolides; Bufonidae; Digitalis; Digitalis Glycosides; Heart; Hedera; Venoms